Poly(trimethylene terephthalate), also known as poly(propylene terephthalate), or, less formally, as “3GT” polymer, is well known in the art. The properties and manufacturing thereof are described by Chuah in The Encyclopedia of Polymer Science, on-line, DOI 10.1002/0471440264.pst292.
J. C. Chang et al., U.S. Pat. No. 6,923,925, describes a composition comprising poly(trimethylene dicarboxylate), especially poly(trimethylene arylate), most especially poly(trimethylene terephthalate) (PTT), with 0.01-10% by weight of preferably high molecular weight polystyrene (PS) dispersed within the poly(trimethylene dicarboxylate), and having a PS particle size of less than 2 micrometers (μm). Only compositions in the concentration range of 1-2% PS are exemplified. It was found that PTT compositions comprising 1-2% by weight of PS, on the basis of total polymer weight, were capable of melt spinning into fiber at spinning speeds significantly higher than that achievable with PTT without PS. The manner by which the compositions were prepared was by co-feeding pellets of the two polymers into a twin screw extruder or by making a salt and pepper blend of pellets of the two polymers in the desired proportions and then feeding the resulting pellet mixture into a twin screw extruder. The extrudate was extruded as a strand and chopped into pellets. These blend pellets were then fed to a spinning machine to melt spin fiber.
U.S. Pat. No. 4,475,330 discloses a polyester multifilament yarn made from polyester filaments consisting essentially of (a) a copolymer of two or more monomers selected from the group consisting of ethylene terephthalate, trimethylene terephthalate and tetramethylene terephthalate, and/or (b) a blend of two or more polymers of ethylene terephthalate, trimethylene terephthalate and tetramethylene terephthalate. This patent describes blends of polyesters with 3 to 15% of non-crystalline polymer, preferably styrene polymers or methacrylate polymers.
The process of Chang et al., op. cit., was developed to produce poly(trimethylene dicarboxylate) yarns, particularly partially oriented yarns, at high spin speeds. The advantages of the invention were obtained using a blend comprising poly(trimethylene dicarboxylate) and (PS). Achievement of commercial scale operation of the process of Chang et al., may present several problems. It could be very expensive to transition a commercial scale continuous melt polymerizer from a PTT product containing PS to a PTT product not containing PS. Employing a side-stream extruder and feeding in the required amount of PS to arrive at a 1% PS composition could require specially designed equipment to feed in the small proportion of PS needed.
There remains a need for films exhibiting improved toughness and increased opacity over films of neat poly(trimethylene arylate) polymers such as provided by the present invention.